The invention relates to articles having a coextruded biaxially oriented, heat-set polyester support film. More particularly, the invention relates to articles prepared utilizing this support film, e.g., pressure-sensitive tapes, coated abrasive sheet material, butt-splicing tapes for belts such as coated abrasive belts, and lithographic printing plates.
Numerous sheet-like or layered articles which employ a backing layer of a tough flexible material are known. Typical examples include coated abrasive sheets, pressure-sensitive adhesive tapes, photographic film, magnetic recording tape, etc. The backings employed typically include paper, metal foil, cloth, film-forming plastic material, and the like.
Biaxially oriented and heat-set films of highly crystalline polymeric materials such as polyethylene terephthalate (PET), polycyclohexanedimethyl terephthalate (PCDT) and polyethylene naphthalate (PEN) are particularly attractive candidates for coated sheet material backings because of their high tear-resistance, dimensional stability, chemical resistance, wear resistance, strength, abrasion resistance and temperature stability. Such films, however, typically have a smooth, tough, abrasion-resistant, chemical-resistant, dense surface to which conventional adhesive materials bond only with difficulty. Numerous attempts have been made to render the surface of such films more receptive to coatings. While many of these attempts have some merit, none has produced a film which is substantially universally receptive to a wide variety of coating materials.
One method employed to make such films more receptive is to roughen their surfaces by mechanical or chemical means. Mechanical roughening involves making minute cuts into the surface of the film, tending to weaken it structurally. Chemical treatments with strong acids or bases are generally undesirable because they not only tend to degrade the polymer and weaken the film but also are extremely toxic and hazardous to use. A commerically useful chemical treatment of PET film with a non-degrading solvent is disclosed in Krogh et al. U.S. Pat. No. 3,607,354 wherein the chemical treating agent is a hydroxybenzene derivative solvent such as parachlorophenol, but the process requires an extra treating step and necessitates solvent removal.
Another method of making the surface of oriented heat-set films more receptive to coatings is to apply a primer layer of a chemically related but more coating-receptive material by solvent casting or lamination. Because of the unreceptive nature of the surface of biaxially oriented heat-set PET, PCDT and PEN films, even these primer coatings tend to easily delaminate, producing products which have at best, a very short useful life. U.S. Pat. No. 2,961,365 discloses such conventional techniques for coating polyester compositions on biaxially oriented, heat-set PET films.